1. Field of the Invention
This invention relates generally to a method for determining a rate of application of fertilizer. More particularly, but not by way of limitation, the present invention relates a method for in-season macro and micronutrient application using within-element-size coefficient of variation to improve a prediction of yield potential, and hence, to more accurately predict the nutrient requirements of the crop.
2. Background
Presently, there is a need for a convenient method to determine the amount of fertilizer required to optimize the yield of a particular crop. While soil samples may be analyzed to determine the soil condition, the process is neither convenient nor is it conducive to advanced farming techniques such as precision farming.
“Precision farming” is a term used to describe the management of intrafield variations in soil and crop conditions. “Site specific farming”, “prescription farming”, and “variable rate application technology” are sometimes used synonymously with precision farming to describe the tailoring of soil and crop management to the conditions at discrete, usually contiguous, locations throughout a field. The size of each location depends on a variety of factors, such as the type of operation performed, the type of equipment used, the resolution of the equipment, as well as a host of other factors. Generally speaking, the smaller the location size, or plot, the greater the benefits of precision farming, at least to areas of approximately one-half square meter.
Typical precision farming techniques include: varying the planting density of individual plants based on the ability of the soil to support growth of the plants; and the selective application of farming products such as herbicides, insecticides, and, of particular interest, fertilizer.
In contrast to precision farming, the most common farming practice is to apply a product to an entire field at a constant rate of application, often based on a predicted crop yield. The rate of application is selected to maximize crop yield over the entire field. Unfortunately, it would be the exception rather than the rule that all areas of a field have consistent soil conditions and consistent crop conditions. Accordingly, this practice typically results in over application of product over a portion of the field, which wastes money and may actually reduce crop yield, while also resulting in under application of product over other portions of the field, which may also reduce crop yield.
Perhaps even a greater problem with conventional methods is the potential to damage the environment through the over application of chemicals. Excess chemicals, indiscriminately applied to a field, ultimately find their way into the atmosphere, ponds, streams, rivers, and even the aquifer. These chemicals pose a serious threat to water sources, often killing marine life, causing severe increases in algae growth, leading to eutrophication, and contaminating potable water supplies.
From the early 1950's through the early 1970's, increased food production was a priority in agricultural circles around the world. During this period it was noted that nitrogen fertilizer had the single largest impact on yield and, as a result, the largest increase in the use of agricultural inputs has been nitrogen. Although fertilizer nitrogen consumption and grain production have both increased over the last five decades, contamination of surface water and ground water supplies continues because the efficiency at which fertilizer nitrogen is used has remained at a stagnant, and dismal, 33%, worldwide. While the unaccounted for nitrogen (67% of applied fertilizer nitrogen) has been well documented, heretofore, there has been no significant improvement on the inefficiency at which nitrogen is used in cereal production.
Thus it can be seen that there are at least three advantages to implementing precision farming practices. First, precision farming has the potential to increase crop yields, which will result in greater profits for the farmer. Second, precision farming may lower the application rates of seeds, herbicides, pesticides, and fertilizer, reducing a farmer's expense in producing a crop. Finally, precision farming will protect the environment by reducing the amount of excess chemicals applied to a field, which may ultimately end up in a pond, stream, river, and/or other water source.
Predominately, precision farming is accomplished by either: 1) storing a prescription map of a field wherein predetermined application rates for each location are stored for later use; or 2) by setting application rates based on real-time measurements of crop and/or soil conditions. In the first method, a global positioning system (GPS) receiver, or its equivalent, is placed on a vehicle. As the vehicle moves through the field, application rates taken from the prescription map are used to adjust variable rate application devices such as spray nozzles. A number of difficulties are associated with the use of such a system, for example: due to the offset between the GPS receiver and the application device, the system must know the exact attitude of the vehicle in order to calculate the precise location of each application device, making it difficult to achieve a desirable location size; soil and plant conditions must be determined and a prescription developed and input prior to entering the field; and resolving a position with the requisite degree of accuracy requires relatively expensive equipment.
In the latter method, a sensor is used to detect particular soil and plant conditions as the application equipment is driven through the field. The output of the sensor is then used to calculate application rates and adjust a variable rate application device in real time. Since the physical relationship between the sensor and the application device is fixed, the problems associated with positional based systems (i.e., GPS) are overcome. In addition, the need to collect crop data prior to entering the field is eliminated, as is the need for a prescription map.
With either technique, there is a need to sense the soil and/or crop conditions in order to determine a rate of application of a given farm product. With regard to soil analysis, attempting to analyze the soil condition by way of a soil sample at each site would be time consuming and the handling of individual samples would be a logistical nightmare. Even with in-field analysis, the task would be daunting, at best.
Co-pending U.S. patent application Ser. No. 10/195,138, filed by Raun, et al., which is incorporated herein by reference, describes a method for determining in-season macro and micronutrient application based on predicted yield potential and a nutrient response index. With the method of Raun, et al., remote sensing may be employed to determine plant need for a particular nutrient and to determine mid-season yield potential. An optical sensor is used to measure the reflectance of a target plant at one or more wavelengths of light and, based on known reflectance properties of the target, an output is provided which is indicative of the need for the nutrient. The specific need is determined from a response index for the field, which is calculated by scanning a nutrient rich reference strip and a reference strip fertilized according to the common practice for the field. It has been found that the method of Raun, et al. provides increased yield with overall lower fertilizer application rates with plot sizes as small as 0.4 square meters.
Research also suggests that the coefficient of variation (“CV”) for plant conditions within a particular plot provides meaningful insight into the nutrient requirements for the plot. The coefficient of variation is defined as the standard deviation divided by the mean times one hundred (given in percentage). Generally speaking, plot size is ideally that area which provides the most precise measure of the available nutrient, where the level of nutrient changes with distance. CV, on the other hand, provides an indication of variability within a plot, which is likely due to factors other than nutrient availability.
Thus it is an object of the present invention to provide a convenient method for determining an application rate for the in-season application of nutrients, which is non-invasive to growing crops and is conducive to advanced farming techniques.
It is a further object of the present invention to refine previous precision farming techniques, using the coefficient of variation, to further improve nutrient application rates.